NiCoP based carbon nanotube heterostructure for improved oxygen redox reaction kinetics in Li-O2 batteries

Abstract

The design of ultra-stable cathode materials of Li-O2 batteries with excellent catalytic performance is very important and desirable. However, some problems such as sluggish electrochemical reaction kinetics and unwanted side reactions still remain challenging. Carbon materials own hierarchical porous structure which facilitates mass transport and accommodates discharge products but are not stable enough as cathode of Li-O2 batteries. Here in, we fabricated a unique NiCo bimetallic phosphide combined with carbon nanotube heterostructure (abbreviated as NiCoP/CNT) by hydrothermal method. Density functional theory (abbreviated as DFT) calculation demonstrates that bimetallic phosphide NiCoP/CNT delivered much better electrical conductivity, greater adsorption to reactants, and more electron transfer with discharge products Li2O2, compared to monometallic phosphides CoP and Ni2P. Therefore, NiCoP/CNT based cathode displayed low overpotential of 0.87 V at current of 100 mA g−1 with a fixed specific capacity of 1000 mAh g−1 and run steadily over 150 cycles under high current of 500 mA g−1 with a fixed specific capacity of 1000 mAh g−1. Furthermore, Ex-situ X-ray Photoelectron Spectroscopy and in-situ differential electrochemical mass spectroscopy proved the existence of intermediate products Li2-xO2. This approach provides a reference for designing and synthesis of bimetallic cathode in Li-O2 batteries.